Formats for the exchange of bibliographic data use the ISO 2709 record structure which started out as the structure for the Library of Congress MARC format. The UNISIST Reference Manual was an early international exchange format developed by ICSU‐AB and Unesco and included cataloguing rules suitable for use by A & I Services. The national libraries developed UNIMARC under IFLA auspices as their exchange format since the national formats were not totally compatible. Unesco, concerned about the lack of compatibility between the major international exchange formats, sponsored a symposium, resulting from which a Common Communication Format was developed and ISO began work on a data element directory. International formats also exist for nuclear and agricultural information as well as for serials data. Other formats exist which are used internationally and have different structural characteristics. The International MARC Network Study Steering Committee has taken an interest in the exchange of bibliographic data and has organized a test of UNIMARC and supervised a UNIMARC Handbook to clarify the format. International exchange formats tend to acquire accompanying cataloguing rules: indeed they will only be really effective if there are internationally accepted cataloguing rules and authority files.